Stripper finger

ABSTRACT

Stripping apparatus for stripping electrostatically tacked copy sheet from a xerographic drum in which a stripping finger is positioned on a pivot axis to extend tangentially to the drum surface with the tip portion of the finger extending a predetermined extent from the drum surface. A counterweight is mounted on the opposite side of the pivot axis to edge the finger into a low pressure riding contact with the drum surface to effect stripping of the copy sheet from the drum surface at very low compressible stresses and without abrading the drum surface. The finger pivot is arranged to absorb most of the impact of stripping. To effect this, the bearing area at the center of the pivot is kept to a minimum to enable the finger to be self aligning, thereby equalizing pressure while the finger is maintained in contact with the drum surface. The counter-weight is adjustable for varying the pressure of the finger member against the drum surface.

United States Patent [191 Schmalzbauer 1 STRIPPER FINGER [75] Inventor: Herbert F. Schmalzbaucr, Chester,

Conn.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Apr. 25, 1973 [21] Appl. No.: 354,551

Related US. Application Data [63] Continuation of Serv No. 247,064, April 24, 1972,

Primary Examiner-James B. Marbert Assistant Examiner-Bruce H. Stoner, Jr.

[57] ABSTRACT Stripping apparatus for stripping electrostatically tacked copy sheet from a xerographic drum in which a stripping finger is positioned on a pivot axis to extend tangentially to the drum surface with the tip portion of the finger extending a predetermined extent from the drum surface. A counterweight is mounted on the opposite side of the pivot axis to edge the finger into a low pressure riding contact with the drum surface to effect stripping of the copy sheet from the drum surface at very low compressible stresses and without abrading the drum surface. The finger pivot is arranged to absorb most of the impact of stripping. To effect this, the bearing area at the center of the pivot is kept to a minimum to enable the finger to be self aligning, thereby equalizing pressure while the finger is maintained in contact with the drum surface. The counter-weight is adjustable for varying the pressure of the finger member against the drum surface.

2 Claims, 4 Drawing Figures PATENIED m2? m5 SHEET FIG. I

STRIPPER FINGER This is a continuation of application Ser. No. 247,064, filed Apr. 24, 1972, now abandoned.

BACKGROUND OF THE INVENTION This invention generally relates to xerography, and in particular, to apparatus for stripping a paper support material having an electrostatically transferred toner image thereon from a moving photoconductive surface.

More specifically, this invention relates to apparatus which is particularly well adapted to removing an insulating paper copy sheet having an electrostatically transferred toner image loosely adhered thereto from the top surface of a moving photoconductor.

In conventional xerography, a photoconductive surface is uniformly charged and the charged surface then exposed to a light image of an original to be reproduced. Under the influence of the light image, the charge on the surface is selectively dissipated to produce what is known as a latent electrostatic image. The charged latent image is developed, or made visible, by attracting oppositely charged toner particles, which are brought into close proximity to the plate surface, into the image areas. The developed image is then generally transferred to a paper support material and the image affixed thereto to form a permanent record of the original document.

The copy sheet is placed over the image bearing photoconductive surface and the backside of the sheet subjected to a spray of ionized air. A charge is built up on the sheet having a magnitude and polarity sufficient to electrostatically attract the toner particles from the photoconductive surface to the copy sheet. However, during transfer, a charge opposite to the charge found in the nonimaged areas on the drum surface is induced in the paper causing the copy sheet to become electrostatically tacked to the drum surface. Removal of the copy sheet and the toner image loosely adhering thereto has long been a problem in the xerographic art.

One of the best known and most widely used stripping device is the mechanical air puffer. The copy sheet is stripped from the surface by introducing a stream of air between the copy sheet and the surface and then allowing the sheet to fall away from the photoconductor surface where it can be picked up by a transport belt or the like. While puffing devices are satisfactory in some respects they are not entirely reliable in operation.

Another stripping device is an array of mechanical fingers which are actuated by an electrical signal into contact with the photoconductor surface so as to contact the paper edge and wedge the edge away from the photoconductive surface. Normally these stripping fingers are made out of plastic materials or are plastic coated to prevent scoring or abrading the photoconductive surface. It has been found, however, that due to the constant actuating into contact and away from the drum surface that the fingers wear quickly requiring frequent replacement due to the fact that they cannot remain in their sharp configuration which is necessary for the wedging effect. An example of a mechanical stripping finger is described in US. Pat. No. 3,578,859. The present invention is an improved stripping finger over existing stripping fingers.

It is therefore a primary object of this invention to improve apparatus for removing an electrostatically tacked image bearing support material from a moving photoconductive surface.

It is a further object of this invention to remove electrostatically tacked copy sheet from a moving photoconductive surface without scoring or abrading the surface.

It is a further object of the present invention to effect greater reliability in stripping copy sheet from photoconductive surfaces.

It is still a further object of the present invention to provide a simplified design and construction for a stripping finger which remains in contact with the photoconductive surface at all times.

It is yet another object of this invention to effect paper stripping by a mechanism which does not require timing and is independent of the paper position on a photoconductive surface.

It is yet another object of the invention to produce an inexpensive manufacture and assembly for mechanically stripping copy sheet from a photoconductive surface.

Another object of the invention is to enable the stripping finger to pivot to absorb most of the impact of stripping and be self aligning, thus equalizing pressure at the line of contact with the photoconductive surface.

These and other objects as well as other features of the present invention are attained by positioning a single elongated metallic finger extending tangentially to the photoconductive surface with the tip beyond the surface and by maintaining the finger against the photoconductive surface at a very low contact pressure.

For a better understanding of the present invention as well as other objects and features thereof reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 illustrates schematically a xerographic reproducing apparatus employing a preferred embodiment of the paper stripping apparatus of the present invention;

FIG. 2 is a side elevation sectional view of the stripping assembly of the invention;

FIG. 3 is a plan view of the stripping assembly shown in FIG. 2; and

FIG. 4 is an enlarged side elevation of the stripping assembly illustrating the mechanism employed for stripping a copy sheet from the xerographic drum surface.

For a general understanding of the illustrated copier/reproduction machine, in which the invention is incorporated, reference is had to FIG. 1 in which the various system components for the machine are schematically illustrated. As in all electrostatic systems such as a xerographic machine of the type illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image, corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface to which it is fused by a fusing device whereby the powder image is caused permanently to adhere to the support surface.

In the illustrated machine, an original to be copied is placed upon a transparent support platen P fixedly arranged in an illumination assembly and image rays are projected by means of an optical system for exposing the photosensitive surface of a xerographic plate in the form of a drum generally indicated by the reference numeral 10.

The drum is mounted upon the frame of the machine and is adapted to rotate in the direction of the arrow at a constant rate. During this movement of the drum, it passes a charging station A where a uniform electrostatic charge is applied to the surface thereof. Next at an exposure station E exposure of the drum surface to the light image discharges the xerographic plate in the areas struck by light, whereby there remains on the surface a latent electrostatic image in image configuration corresponding to the light image projected from the original on the supporting platen. As the drum surface continues its movement, the electrostatic image passes through a developing station C in which there is positioned a developer assembly. The developer assembly deposits developing material to the upper part of the drum whereat the material is directed to cascade over the drum surface in order to provide development of the electrostatic image. As the developing material is cascaded over the drum surface, toner particles in the development material are deposited on the surface to form powder images.

The developer electrostatic image is transported by the drum to a transfer station D whereat a sheet of copy paper is moved at a speed in synchronism with the moving belt in order to accomplish transfer of the developed image. There is provided at this station a sheet transport mechanism adapted to transport sheets of paper from a paper-handling mechanism to the developed image on the drum at the station D.

After the sheet is stripped from the drum by a stripping assembly 20 as will be described more fully hereinafter, it is conveyed to a fuser apparatus generally indicated by the reference numeral whereat the developer and transferred xerographic powder image on the sheet material is permanently affixed thereto. After fusing, the finished copy is discharged from the apparatus by a belt conveyor to a suitable point for collection externally of the apparatus.

Suitable drive means are arranged to drive the drum in conjunction with timed exposure of an original to be copied, to effect conveying and cascade of toner material, to separate the feed sheets of paper and to transport the same across the transfer station D and to convey the sheet of paper through the fuser apparatus in timed sequence to produce copies of the original.

It is believed that the foregoing description is sufficient for the purposes of this application to show the general operation of an electrostatic copier using an illumination system constructed in accordance with the invention. For further details concerning the specific construction of the electrostatic copier, reference is made to U.S. Pat. No. 3,301,126 filed Sept. 30, 1964 in the name of Osborne et al.

As shown in FIGS. 2-4 a stripping assembly comprises a frame 22 on which is mounted a pin member 24 which forms a pivot axis for stripping finger assembly 26. Stripping finger assembly 26 includes an elongated support member 28 which receives pin member a 24 through a counterbore opening 29 having a bearing surface 27 having a thickness of about 0.050 inches for a purpose to be described. An elongated stripping finger 30 is mounted on the support member by one or more screw members 34. It will be noted that the elongated stripping finger 30 extends tangentially to the drum surface with the tip 32 extending slightly past the point of tangency at the drum surface by a distance x and above the drum surface by a distance y (FIG. 4) such that no abrading or damage of the drum surface can occur. The distance y is sufficiently small such that it can peel the edge of paper from the drum surface. It has been found that this distance should be no greater than one half the thickness of the paper. Desirably the stripping finger 30 is made out of a hardened tool steel material for high durability and good surface finish. Any suitable material may be used for this purpose such as tool steel with hardness specification of RC -65. The support member 28 desirably is made out of light weight material such as aluminum.

The stripping finger 30 is maintained at all times into low pressure contact with the drum surface. To effect this, a counterweight assembly 35 is mounted on the stripping finger assembly to effect the proper weight distribution and position of the finger. The counterweight assembly 35 includes a weight member 38 which is threaded on a support member 39. The pressure at which the finger is maintained into contact with the drum surface may be varied by changing the posi-' tion of the weight 38 on threaded member 39. It will now be appreciated that the pivot of the stripping finger absorbs most of the impact during the stripping operation. By virtue of the counterbore opening 29 and bearing surface 27 the stripping finger is self aligning, thus equalizing the pressure at the line of contact with the drum surface.

The stripping finger 30 strips the leading edge of the sheet from the drum surface. As the sheet is stripped fromthe drum stationary support fingers 40 engage the leading edge of the sheet being stripped and serve to guide the sheet downwardly into contact with the vacuum transport 42. Stationary fingers 40 may be ad justed relative to the stripping finger assembly and drum surface by means of screws 46.

In this manner copy sheet is stripped from a photoconductive surface by a stripping finger which is simple and inexpensive yet is reliable in the stripping operation. More than this, no scoring or abrading of the drum surface and accompanying deterioration of copy quality is incurred. It will be appreciated that the stripping finger of the present invention is a significant advance in the copying arts and in particular is highly advantageous over the existing stripping devices used in xerographic copying machines.

What is claimed is:

1. In a xerographic copying apparatus wherein an insulating copy sheet is electrostatically tacked to a moving xerographic drum image bearing surface, an improved stripping apparatus for removing the tacked copy sheet from the moving drum surface comprising a frame,

a support member mounted about a pivot axis on said frame,

an elongated finger member mounted on said support member extending tangentially to the drum surface with its tip portion extending a predetermined extent beyond the point of tangency,

counterweight means mounted on said support member on a side of said pivot axis opposite said finger member to urge said finger member into low pressure riding contact with the drum surface whereby the copy sheet is stripped from the drum surface at very low compressive stresses,

wherein the support member is formed with a counter-bore opening about the pivot axis to present a minimum of pivot bearing surface to effect self aligning of the finger member at the line of contact with the drum surface.

2. In a xerographic copying apparatus wherein an insulating copy sheet is electrostatically tacked to a moving xerographic drum image bearing surface, an improved stripping apparatus for removing the tacked copy sheet from the moving drum surface comprising a frame,

a support member pivotally supported on said frame,

an elongated finger member mounted on said support member extending tangentially to the drum surface with its tip portion extending a predetermined extent beyond the point of tangency,

counterweight means mounted on said support member on a side opposite said finger to urge said finger into low pressure riding contact with the drum surface whereby the copy sheet is stripped from the drum surface at very low compressive stresses;

wherein said counterweight means includes a threaded member for adjusting the pressure of the finger member against the drum surface. 

1. In a xerographic copying apparatus wherein an insulating copy sheet is electrostatically tacked to a moving xerographic drum image bearing surface, an improved stripping apparatus for removing the tacked copy sheet from the moving drum surface comprising a frame, a support member mounted about a pivot axis on said frame, an elongated finger member mounted on said support member extending tangentially to the drum surface with its tip portion extending a predetermined extent beyond the point of tangency, counterweight means mounted on said support member on a side of said pivot axis opposite said finger member to urge said finger member into low pressure riding contact with the drum surface whereby the copy sheet is stripped from the drum surface at very low compressive stresses, wherein the support member is formed with a counter-bore opening about the pivot axis to present a minimum of pivot bearing surface to effect self aligning of the finger member at the line of contact with the drum surface.
 2. In a xerographic copying apparatus wherein an insulating copy sheet is electrostatically tacked to a moving xerographic drum image bearing surface, an improved stripping apparatus for removing the tacked copy sheet from the moving drum surface comprising a frame, a support member pivotally supported on said frame, an elongated finger member mounted on said support member extending tangentially to the drum surface with its tip portion extending a predetermined extent beyond the point of tangency, counterweight means mounted on said support member on a side opposite said finger to urge said finger into low pressure riding contact with the drum surface whereby the copy sheet is stripped from the drum surface at very low compressive stresses; wherein said counterweight means includes a threaded member for adjusting the pressure of the finger member against the drum surface. 